Thread brake

ABSTRACT

A thread brake includes a horizontal abrasion-resistant stripshaped flexible overlay on a resilient backing, pivotally supported about a horizontal axis at the half height of the strip, and a plurality of cylindrically curved braking elements supported at the ends of levers on a common shaft about which the levers are rotated to engage successively against the overlay. In another embodiment the strip is rocked about an axis displaced from itself into engagement with stationary braking elements.

United States Patent [72] Inventor Erwin Pfarrwaller Winterthur, Switzerland [2]] Appl. No. 868,165 [22] Filed Oct. 21, 1969 [45] Patented Jan. 11, 1972 [73] Assignee Sulzer Brothers Limited Winterthur, Switzerland [32] Priority Oct. 23, 1968 [33] Switzerland [31] 15884/68 [54] THREAD BRAKE 8 Claims, 5 Drawing Figs.

[52] US. Cl l88/65.l, 139/122 R, 188/652, 226/176, 242/149 [51] Int. Cl B6511 59/16, D03d 47/00 [50] Field of Search 24/245 E, 262, 263.4; 139/122 R, 126, 194; 188/651, 65.2; 226/176; 242/149; 271/23; 274/1 1 [56] References Cited UNITED STATES PATENTS 1,386,813 8/1921 Townsend l88/65.1

2,489,632 11/1949 Freider et al. l88/65.l X 2,519,107 8/1950 Brown 24/262 2,749,946 6/1956 Pfarrwaller... 139/ l 26 2,819,736 H1958 Pfarrwaller... 139/194 2,877,012 3/1959 Angel et al 188/65.l X 3,078,367 l/l963 Jackson 24/262 3,181,569 5/1965 Carroll 139/122 R 3,348,582 10/1967 Brookshire 139/122 R 3,393,712 7/1968 Fransen 188/651 X FOREIGN PATENTS 1,151,230 7/1963 Germany 139/122 R Primary Examiner-Milton Buchler Assistant Examiner-Stephen G. Kunin Attorney-Pennie, Edmonds, Morton, Taylor and Adams ABSTRACT: A thread brake includes a horizontal abrasionresistant strip-shaped flexible overlay on a resilient backing,

pivotally supported about a horizontal axis at the half height of the strip, and a plurality of cylindrically curved braking elements supported at the ends of levers on a common shaft about which the levers are rotated to engage successively against the overlay. In another embodiment the strip is rocked about an axis displaced from itself into engagement with stationary braking elements.

PMENTEB JAM 1 [12 SHEET 1 OF 3 MVen/or: Erwin Pforrwoller ATTORNEYS PATENTED JAN! 1 M2 SHEET 2 [1F 3 T H. EJJ

//Il//I/0/.' Erwin Pforrwoller BY W ATTORNEYS THREAD BRAKE The present invention pertains to a thread brake for use in looms, having two cooperating braking members or elements, at least one of which is flexible and between which the thread to be braked is engaged for frictional engagement and braking action therewith.

It has been proposed to provide a thread brake including a flexible brake element in the form of a loop-shaped band or strip running over two rolls and kept tensioned by a spring for example. The band is advanced by the two rolls in order to prevent the thread from wearing away the brake element on one side. In order to brake the yarn gently, several tensioned brake bands of this type have been arranged one after the other, each cooperating with an associated brake element. The brake bands and their springs and driving elements must each be precisely adjusted and occasionally readjusted or replaced.

In looms in which several different wefts, for example, two, four or six wefts of different colors are picked in turn, a separate thread brake is generally provided for each weft thread. If a multiple weft loom of this type has the corresponding number of thread brakes of the previously proposed type, a fairly large number of moving parts must be checked and controlled.

It is an object of the invention to provide a simplified weft brake having a reduced number of parts. The invention provides such a brake in which the portion of the flexible brake element which touches the thread is very light so that, for example when braking a thread of uneven thickness or when the thread contains knots, the element can move away from the braking position to an extent determined by the uneven thickness of the thread and can then return to the braking position when the thread regains its normal thickness so that a constant braking effect is obtained.

According to the present invention a thread brake has two cooperating braking elements, at least one of which is yieldable and includes an underlay of a resilient material and an overlay having a braking surface arranged to contact the thread, the braking surface comprising a material which has greater wear resistance to the passage of the thread thereacross than has the underlay. The overlay adapts itself to the contours of the braking element, cooperating with it to increase the effective braking area, so that threads are gently braked.

In order to retain the resilience of the yieldable brake element constant for as long an operating time as possible, the underlay is preferably made of a foamed material.

Conveniently, the overlay is flexible by reason of its shape and has a lining of abrasion-resistant material, e. g., chromium or ceramic or metal-ceramic on the side thereof forming the braking surface.

The overlay may alternatively be of hardened steel and may have a thickness of approximately 0.02 to 0. 1 mm.

In order to vary the braking effect of the thread brake during loom operation, one of the two cooperating braking elements may be movable. It may be operatively connected either to a cam drive or to an electromagnet controlled in accordance with a predetermined operating program.

Particularly gentle braking of the thread is obtained when, in accordance with a further feature of the invention, at least one of the braking elements is divided into a plurality of parts which are situated successively along the path taken by the thread, each part being mounted so that it can be separately adjusted and fixed in relation to the braking element with which it cooperates. The braking effect as a whole is therefore the sum of separate partial braking actions, each exerting a small local force, and the stress on the thread is consequently small.

Conveniently when the brake is off the distances between the parts of one braking element and the brake elements cooperating with them are unequal. By setting the brake in this manner, the braking forces acting on the thread can be increased in stages. This is a great advantage, for example, when braking a fine, delicate yarn or a yarn containing loose knops.

The path of the thread is precisely fixed in accordance with a further feature of the invention, preferably along the middle of the available braking area, by the provision of guide elements for the thread.

Further provision for adjustment of the braking action is made in accordance with a further feature of the invention by the provision of a plurality of thread guide elements arranged in positions offset from a line corresponding to the shortest path of the thread through the brake, so that the guide elements form deflection points for the path of the thread, whereby the thread extends through the brake on a line which is not straight. The friction which arises because the thread wraps itself round part of the guide elements provides additional braking of the thread, to an extent depending on the number of deflection points and on their angles of wrap.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described in terms of a number of exemplary embodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a vertical elevation, partly in section, of a thread brake according to the invention;

FIG. 2 is a side view of the brake of FIG. 1 looking in the direction of the arrow II of FIG. 1;

FIG. 3 is a plan sectional view on the line III-III in FIG. 2;

FIG. 4 is a vertical sectional view on the line lV-IV in FIG. 2; and

FIG. 5 shows a modified form of thread brake.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 2, a U-shaped yoke I is fixed, with its limbs pointing upwards, to the frame of a loom (not shown). The yoke carries a braking element 2 with a substantially vertical braking surface and a braking element 3 consisting of three brake fingers 3a, 3b and 30 which are pivotable relative to and against the brake element 2. The braking element 2 includes a horizontal beam 4 made from channebshaped sheet metal, the open side of the channel facing the brake fingers 3a to 3c. The ends of the beam 4 are attached by screws 5 to brackets 6 which are adjustably mounted on the free ends of the limbs of the yoke l by means of screws 7. These screws 7 are so arranged that their longitudinal axes are situated on a line approximately at the half height of the beam 4. The beam 4 can pivot about this line and be thereby adjusted to any angle to the vertical.

Opposite each brake finger 3a to 3c, the edges or flanges of the channel-shaped beam 4 have recesses or notches 8 formed therein so that the associated finger can enter the channel defined by the beam 4 without touching the flanges thereof. Two cylindrical guide pins 9 and 9, made from sintered aluminum oxide, are set in the web of the beam 4 on the center line thereof. The pins project beyond the flanges of the beam 4 on the concave side of the beam (FIG. 3).

A soft resilient underlay or pad 12 is placed in the channel formed by the beam 4, substantially filling it. An overlay I1 is fastened to the underlay I2, for example by means of an adhesive, the overlay being in sheet form and consisting of hardened steel sheet which may for example be some 0.07 mm. thick. The thickness of the overlay I1 depends on the type of thread to be braked and on the underlay 12. It may, for example, be between 0.02 and 0.1 mm. or more thick. The overlay 11 and underlay 12 contain apertures for the passage of the pins 9, 9.

The underlay I2 may take the form of a pad of foam material and may be approximately 8 mm. thick. The foam material may be a polyether foam. Of course however a foam pad of other thickness and of other plastic material or of rubber may be used.

The underlay 12 with its adherent overlay ll lies loosely in the beam 4, and lugs 13 on the brackets 6 prevent it from falling out. The underlay may be bowed so that when placed in the channel its ends bear resiliently against the inner side of the lugs 13.

The two brackets 6 are fitted with eyes, indicated at 14 and 14', substantially at the height of the centerline of the beam 4. The thread to be braked,'which comes for example from a weft supply bobbin (not shown), passes through the eye 14 and then along the overlay 11 and over the projecting ends of the two pins 9 and 9 to the eye 14', and through this eye to the picking mechanism of the loom.

The brake fingers 3a to 3c are in the form of pivoted levers adjustably mounted on a common shaft 18 by means of two jaws 17 for each finger, the jaws being clamped together by means of a screw 19. That portion of each finger which cooperates with the overlay 11 to function as a brake has a braking surface 16 conforming substantially to a fraction of a cylinder with an axis parallel to the long dimension of the finger and with a height slightly greater than the width of the beam 4. The fingers 3a to 30 are positioned on the shaft 18 so that their braking surfaces 16 enter the recesses 8 during operation and extend over the entire width, i.e., vertical height, of the overlay 11. Each of the braking surfaces 16 is coated with an abrasion-resistant, metal-ceramic layer of aluminum oxide.

The shaft 18 is mounted in two bearings 20 attached to the limbs of the yoke 1. One end of the shaft carries, outside the yoke 1, a lever 21 loosely pivoted thereon and having formed therein a groove 22 whose sides run parallel to the longitudinal axis of the shaft 18. This groove 22 is engaged by a finger 23 forming part of a dog, catch or coupling member 24 which is fixed to the shaft 18 adjacent the lever 21 by means of two jaws 25 (FIG. 4). The jaws 25 are clamped to the shaft 18 by means of a screw 19.

The groove 22 is wider than the finger 23, so that the finger can be moved between the sides of the groove and the shaft 18 can therefore be rotated by a corresponding amount relative to the lever 21. The lever 21 has a blind bore open to the lower side of the groove 22. This bore contains a compression spring 26 which stresses the finger 23 against the upper side of the groove or against a setscrew 27 which extends to the upper side of the groove. The position-of the finger 23 within the groove 22 can be altered by adjustment of the setscrew 27. The free end of the lever 21 is forked, as indicated in FIG. 2, and pivotably connected to one end 50 of a connecting rod 28 (FIG. 1) by means of a pin 42. The connecting rod is swingably and axially displaceable in a guide member 29 mounted on the loom frame. The other end 31 of the rod 28 is pivotally connected, again by means of a pin 42, to a lever 33, mounted for rotation about a shaft 34 carried by the loom frame.

A threaded pin 51 which can be screwed into the connecting rod 28 is attached to the end 50. The pin carries a nut 52 and a loose locknut 53 which can be clamped onto the end of the rod 28. By means of the nut 52, the pin 51 can be rotated and the end 50 can therefore be adjusted lengthwise of the rod 28. Undesired rotation of the pin 51 is prevented by tightening the locknut S3.

A compression spring 30 is engaged about the rod 30 between the other enlarged end 31 of therod and a ring 32 which is loose on the rod but which bears against the fixed guide member 29. Spring 30 stresses rod 28 to the right, in FIG. 1, and thereby tends to rotate the lever 33 clockwise as seen in that figure.

A roller 36 journaled on a stub shaft attached to the lever 33 is stressed by the spring 30 against a cam 37. This cam is mounted on a splined shaft 38 which is connected to the drive of the loom. The lever 33 has an arm 44, to which a stop member 39 is fixed by rivets 45. The member 39 cooperates with an adjustable stop 40 on one end of a pin 41 threaded into a bracket 46 on the base of the loom. The other end of the pin 47 is slotted at 47 and projects from the rear of the bracket 46 to permit axial adjustment of the pin and hence of the stop 40 as indicated by arrows 48.

During operation of the loom, the cam 37, which rotates in the direction of the arrow 49, swings the lever 33 to the left as seen in FIG. 1 while the radius of the cam increases. The lever 21 therefore rotates the shaft 18 clockwise, and the brake fingers 3a to 30 move away from the brake element 2 and the thread 15.

As the radius of the cam decreases, the spring 30 rotates the lever 33 to the right about the pivot 34. The shaft 18 therefore turns counterclockwise, and the brake fingers 3a to 30 again approach the brake element 2. The pivoting motion of the roller lever 33 to the right can be limited by adjusting the stop 40, so that, for example, the roller 36 parts from the profile of the cam 37 at the position where the cam radius is smallest. The left-hand limit positions (FIG. 1) of the fingers 3a to 30, i.e., their braking positions, can therefore be selected either in dependence on or independently of the shape of the cam.

The brake fingers 3a to 30 are so mounted on the shaft 18 by means of the screws 19 that in their left-hand limit positions (braking positions) they deflect the thread 15 and to some extent flex the overlay 11, which is flat when unstressed, and thereby compress the underlay 12. Because the underlay is resilient, the overlay 11 is able to adapt its shape to that of the yarn 15 running along the cylindrical braking surface 16, so that the cross section of the overlay is wavy, as seen in FIG. 3.

The braking positions of the fingers 3a to 3c and the extent of deflections or flexure required are selected according to the type of thread used and the braking effect required. The braking forces acting on the thread may, for example, be of the order of 5 to 200 grams. The depth of penetration of the brake fingers into the channel is varied accordingly. As the fingers move away from the base of the channel the overlay ll springs back into a substantially flat position, due to its own resilience and that of the underlay 12.

In order to insure that the fingers 3a to 3c, when pivoted inwards, engage the thread 15 and not, say, one edge of the overlay 11, the brake element 2 is pivotable about the screws 7 so that the overlay sheet 11 may extend, vertically in FIG. 2, parallel to the generatrices of the cylindrical braking surfaces 16, the latter being assumed to be in the predetermined braking position.

The brake fingers 3a to 30 may be attached to the shaft 18 in slightly different angular positions relative to the lever 21. Then, when the brake is disengaged from the thread, with roller 36 on the high point of cam 37, the distances between the overlay 11, which is flat at this phase of the cycle, and the three braking surfaces 16 are different. These distances may for example decrease in the direction of movement of the thread 15, indicated by arrow 54 in FIG. 2. When the braking process begins, therefore, first finger 3c, then finger 3b and finally finger 3a come into contact with the yarn 15 which is to be braked. Accordingly, the deflection of the overlay 1 1 when the brake is operative is less at the finger 3!; than that at the finger 30, but greater than that at the lever 3a. However, the sequence in which the fingers 3a to 30 engage the thread 15 can be altered as desired.

Since the brake fingers 3a to 30 can be adjusted both as a unit (by shifting the stop 40 or by adjusting at 51, 52, 53 the location of the end 50 and hence the effective length of rod 28, or by rotating the shaft 18 by means of the setscrew 27) and individually, the thread brake can be regulated very accurately, e.g., according to the thread speed and the type of thread used. The brake can thushbe adapted to any operating conditions encountered.

The thread brake is operated in timed relation together with the other components of the loom (not shown). While the brake fingers 3a to 3c are retracted from the brake element 2, the thread 15, a weft, passes from the supply bobbin through the thread brake to the inlet side of the shed and is picked into the shed, for example by a shuttle (not shown). The thread may be drawn off the supply bobbin and through the thread brake at a speed of, for example, 23 meters per second.

During picking, the thread 15 moves between the eyes 14 and 14 in a substantially vertical plane parallel to the overlay 11 (which is flat when the brake is off), following a substantially S-shaped path over the pins 9 and 9' as shown in FIG. 2, at approximately the half height of the braking surface 11. Toward the end of picking, as the radius of cam 37 decreases,

the fingers 3a to 3c pivot into contact with the brake element 2 (FIGS. 1, 3), engaging the taut portions of the thread one after the other in predetermined sequences. The thread 15 is gripped, pressed onto the overlay 11 and so braked and held. In the course of this process the pick is completed and no more thread is drawn off the supply bobbin.

The brake fingers 3a to 3c remain in their left-hand limit position (FIG. 1), as determined either by the smallest cam radius or by the stop 40, until they are set in motion again by further rotation of the cam 37, and a new working cycle begins with a new pick.

The double deflection of the thread 15 round the pins 9 and 9' centers the thread 15 and also provides additional braking. The friction exerted on the thread depends on its angle of wrap around the pins 9 and 9'. The braking action can be reduced if, instead of as shown in FIG. 2, the thread passes from the top of pin 9 over the top of pin 9 to the eye 14'. The angle of wrap will then be less, and so therefore will be the braking force exerted on the thread 15.

Because the brake fingers 3a to 3c are arranged in different angular positions about the axis of shaft 18, the braking action is graded and therefore particularly gentle. Even delicate yarns can be satisfactorily processed. The graded adjustment of the fingers 3a to 3c is also a great advantage when processing knop yarns, i.e., yarns with knotlike lumps and bulges. Such yarns would be damaged by a sudden, simultaneous braking by all three brake fingers, but when the fingers are adjusted as illustrated, only finger 3c comes into contact with the knops at first, initiating preliminary, partial braking of the yarn during which little force is exerted. The braking effect is successively reinforced by fingers 3b and 3a as they come into action one after the other. Since the adjustment of the fingers can be precisely adapted to the thread quality, the stressing of the yarn can be kept low enough to prevent thread breakage. The lightness of the overlay 11, which is due to its small thickness, also helps to prevent yarn breaks. When the knop yarn 15 has already been pushed into contact with the overlay by one of the fingers, the overlay can give in a direction perpendicular to the direction of yarn advance as the knotlike lumps in the yarn pass through, and it then springs back into its original braking position without reducing the braking action.

The thread brake shown in FIG. 5 includes a flexible brake element 2' substantially the same as the element 2 of FIG. 1. This element is fixed by screws 7 to two levers 61, only one of which is visible in FIG. 5. These levers 61, are arranged to rotate as indicated by arrow 63, about a pivot 62 mounted on the loom frame. The pivot 62 is parallel to the direction of advance of the thread 15 which is to be braked. The lower arm of each of the levers 61 is engaged by a tension spring 64 which is attached to the base of the loom and which tends to rotate the lever 61 clockwise about the pivot 62, as seen in FIG. 5. This motion is limited by a stop 65, which can be adjusted relative to the lever 61 and which is mounted on the base of the loom.

The lower end of each of the levers 61 is also connected to an armature 67 of an electromagnet 68 which when energized counteracts the force of the tension spring 64. These electromagnets, shown deenergized in FIG. 5, are connected in a circuit 69 connected by a control device 70 to a source of voltage 77. The control device 70 may be of the type shown in FIG. 6 of applicants U.S. Pat. No. 3,124,166, which is assigned to the assignee hereof and wherein a solenoid is energized by a cam operated switch once per picking cycle of a loom.

A stationary braking element generally indicated at 3 cooperates with the flexible brake element 2' and comprises, much as in FIG. 1, three braking elements 71 situated one behind the other in the direction of advance of the thread 15. These elements 71, only one of which is visible in FIG. 5, are mounted in brackets 74 attached to the loom frame on a line parallel to the pivot 62.

Each element 71 is constructed as a screw with a knurled head 66 and a stem 72. The head 66 has a cylindrical projection 78, coated with an abrasion-resistant, metal-ceramic layer of aluminum oxide and forms a substantially circular. vertical braking surface 16 for the element 71. The edges of the projection 78 are rounded with a relatively large radius to avoid damage to the thread 15, which passes along the braking surfaces 16 approximately halfway up the elements 71.

The stems 72 are screwed into the bracket 74 and are prevented from unintentional rotation by setscrews 75 on the bracket. The bracket 74 may also carry guide elements (not shown) for the thread 15, for example eyes 14 or guide pins 9 and 9 as in FIG. 2.

When the setscrews 75 are loosened, the elements 71 can be rotated about the axes of their stems 72, and the braking surfaces 16' can therefore be adjusted relative to the overlay 1 1.

The right-hand limit position of the levers 61 as seen in FIG. 5 and therefore the braking position of the brake element 2, depends on the adjustment of the stop 65. The brake element 2 can be held to any limit braking position desired, e.g., with the braking surface running vertically, by means of the screws 7.

The elements 71 may be set at different distances from their brackets 74, so that the brake element 2, when brought into its braking position, presses the thread 15 onto the elements 71 in a predetermined sequence, thereby braking the thread. The overlay 11, as in the embodiment described with reference to FIG. 1, is flexed to different extents near the various elements 71, and the underlay 12 is compressed accordingly.

During operation, the electromagnets 68 are alternately energized and deenergized according to a predetermined program, by means of a signal coming from the loom drive by way of the control device and circuit 69. When energized, the electromagnets 68 pull the arrnatures 67 and thereby the lower end of the levers 61 to the right, counteracting the bias of the springs 64, so that the brake element 2' is pivoted out of the position shown and away from the elements 71, and is held in the off position. While the brake is off, the thread 15 is picked as already described with reference to FIG. 1.

Towards the end of the pick, the current to the electromagnets 68 is interrupted upon receipt by the control device 70 of a signal to this effect. The armatures 67 are released, and the springs 64 pivot the levers 61 clockwise back into their limit position, defined by the stop 65. The thread 15 which is to be braked is gripped as already described, and is clamped and braked between the overlay 11 and the brake elements 71. The process is repeated for each pick.

The vertical arrangement of the brake elements simplifies maintenance of the thread brake, since the risk of fouling by fly removed from the thread during braking is substantially reduced. Most of this fly falls off the braking surfaces when the brake is released or can be readily removed by the operator.

In a modification the overlay 11 rests loosely on the underlay 12. It may be made of unhardened steel of some other material, e.g., light metal, titanium or a plastic material, and may be provided with a lining of hard chromium or some other abrasion-resistant material. The lining must be very thin in order to avoid affecting the flexibility of the overlay. For the stresses which occur during yarn braking a ceramic, and more particularly metal-ceramic lining, e.g., of cemented metal carbide or an aluminum oxide, is particularly suitable. The braking surfaces 16 and 16' on the brake elements 3 and 3' being rigid, may have a thicker and therefore more easily produced abrasion-resistant lining.

The brake may have some other number of movable brake elements, for example one, two or more brake fingers, arranged and operated in a similar manner to that in the embodiment illustrated.

In another embodiment, the cooperating elements may be arranged horizontally. Both the cooperating brake elements may be movable. Lastly, both the cooperating brake elements, or a plurality of pairs of brake elements arranged in series, may be flexible.

Iclaim:

l. A thread brake comprising two braking elements, at least one of which is flexible, and means to move said elements toward and away from each other, said flexible element including an elastic underlay and a flexible laminar overlay thereon elastically deformable upon engagement against the other of said elements, said overlay having a wear-resistant material on the side thereof presented to the other of said elements.

2. A thread brake according to claim 1 wherein said underlay is made of a foamed material.

3. A thread brake according to claim 1 wherein said overlay comprises a flexible foil.

4. A thread brake according to claim 1 wherein said overlay comprises a sheet of hardened steel having a thickness between substantially 0.02 and 0.1 mm.

5. A thread brake according to claim 1 including a rotatable cam, and means coupling said cam to said means to move said elements toward and away from each other.

6. A thread brake according to claim 1 including an electromagnet having a movable armature, and means coupling said armature to said means to move said elements toward and away from each other.

7. A thread brake according to claim 1 wherein at least one of said elements includes a plurality of bodies disposed one behind the other along the path of motion of the thread through the brake, and means to adjustably fix the positions of said bodies with respect to each other.

8. A thread brake according to claim 1 including a plurality of guide elements fixed with respect to one of said braking elements.

1! I i l l 

1. A thread brake comprising two braking elements, at least one of which is flexible, and means to move said elements toward and away from each other, said flexible element including an elastic underlay and a flexible laminar overlay thereon elastically deformable upon engagement against the other of said elements, said overlay having a wear-resistant material on the side thereof presented to the other of said elements.
 2. A thread brake according to claim 1 wherein said underlay is made of a foamed material.
 3. A thread brake according to claim 1 wherein said overlay comprises a flexible foil.
 4. A thread brake according to claim 1 wherein said overlay comprises a sheet of hardened steel having a thickness between substantially 0.02 and 0.1 mm.
 5. A thread brake according to claim 1 including a rotatable cam, and means coupling said cam to said means to move said elements toward and away from each other.
 6. A thread brake according to claim 1 including an electromagnet having a movable armature, and means coupling said armature to said means to move Said elements toward and away from each other.
 7. A thread brake according to claim 1 wherein at least one of said elements includes a plurality of bodies disposed one behind the other along the path of motion of the thread through the brake, and means to adjustably fix the positions of said bodies with respect to each other.
 8. A thread brake according to claim 1 including a plurality of guide elements fixed with respect to one of said braking elements. 